Download - ATR FTIR_ Sahana

Transcript

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ATTENUATED TOTAL REFLECTANCE-FTIR

Sahana V

PGD

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Outlook

Internal Reflection Spectroscopy Infrared beam reflects from a interface

via total internal reflectance.

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A little detail

Incident wave Reflected wave

Evanescent wave

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Edge over Traditional methods

Little or no sample preparation Very thin sampling path length Depth of penetration of the IR beam into

sample Sample analysis- faster (less than 1

minute for thick samples)

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How it works

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Factors

Wavelength of IR radiation – λ Refractive indexes of sample and IRE*- n(s), n(IRE) Angle of incidence of IR radiation- θ Depth of penetration(pathlength)- d Sample and IRE contact efficiency

*Internal reflection element

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Instrumentation

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Continued

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3 4

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CRYSTAL MATERIALS

MATERIAL ATR SPECTRA RANGE

REFRACTIVE INDEX

DEPTH OF PENETRATION

USES

Germanium 5,500-675 4 0.66 Good for most samples. Strong absorbing samples, such as dark polymers

Silicone 8,900- 1,500 and 360-120

3.4 0.85 Resistant to basic solutions

AMTIR 11,000-725

2.5 1.77 Very resistant to acidic solutions

ZnSe 15,000-650

2.4 2.01 General use

Diamond 25,000-100

2.4 2.01 Good for most samples. Extremely caustic or harder samples.

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Selecting a right crystal

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Disadvantages

The ATR crystal absorbs energy at lower energy levels

If the sample does not have good contact with the crystal, the data will not be accurate

Most ATR crystals have pH limitations

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Applications

Solid AnalysisLiquid

AnalysisPowder Analysis

excellent technique for measuring the composition of solids

analyze non-aqueous solutions

easier to run by ATR than by IR transmission, because little or no preparation is required

ideal technique for measuring dark colored materials which often absorb too much energy to be measured by IR transmission

Cleanup is easy and fast

pure samples and mixtures that are available in powdered from

films, fabrics, paper, hard polymer sheets, glass, rubber

lubricants, oils, paints, glues, solvents, inks and dyes,Gels and pastes can also be analyzed

pharmaceuticals and pigments

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End Notes

Versatile and non-destructive technique for variety of materials- soft solid materials, liquids, powders, gels, pastes, surface layers, etc.

Useful for surface characterization, opaque samples

Limitations: sensitivity is typically 3-4 orders less than transmission

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References

http://www.azom.com/article.aspx?ArticleID=5958

Perkin-Elmer: Technical Note SpectraTech: Technical Note